Measurement Computing Personal488 rev.3.0 - Manual (Page 45)

Personal488 for Windows 95/98/Me/NT/2000 04-09-01 Hardware Configuration Reference 4-5
Configuring the AT488 Interface DMA Channel
The factory default DMA channel is 5. If this creates a conflict, reset jumpers DACK and DRQ according
to the figure. Both the DRQ and DACK jumpers must be set to the desired DMA channel for proper
operation. If reset, record the new DMA channel being used.
Direct Memory Access (DMA) is a high-speed method of transferring data from or to a peripheral, such as
a digitizing oscilloscope, to or from the PC’s memory. The AT class machine has seven DMA channels.
Channels 0 to 3 (8-bit), 5, 6, and 7 (16-bit) are available only in a 16-bit slot on a PC/AT-class machine.
Channel 2 is usually used by the floppy disk controller, and is unavailable. Channel 3 is often used by the
hard disk controller in PCs, XTs, and the PS/2 with the ISA bus, but is usually not used in ATs. Channels 5
to 7 are 16-bit DMA channels and offer the highest throughput (up to 1 Megabyte per second). Channels 0
to 3 are 8-bit DMA channels and although slower, they offer compatibility with existing GP488B and
GP488B/MM applications that only made use of 8-bit DMA channels. Under some rare conditions, it is
possible for high-speed transfers on DMA Channel 1 to demand so much of the available bus bandwidth
that simultaneous access of a floppy controller will be starved for data due to the relative priorities of the
two channels.